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New Tech Promises EV Charge Times Measured in Minutes

Comparison of Energy Densities for Various Technologies

Researchers at Nanotek Instruments, Inc, and its subsidiary Angstrom Materials in Dayton, Ohio have developed a breakthrough in energy storage design which outpaces supercapacitor and battery technologies. The new devices could not only power long-range and fast charging future electric cars but also provide efficient energy storage capacity to renewable energy sources such as solar, wind and hydro. Called surface-mediated cells (SMCs), the ¬†fundamental breakthrough behind the technology is that it isn’t actually a battery at all. The elegance of the SMC design is that it is not only simpler in design, but already has shown significant increases in energy density and power density despite using less -than-optimized materials and construction. So far, the prototype SMC cells have demonstrated a power density 100 times higher than that of commercial Li-ion batteries and 10 times higher than that of supercapacitors. Power density, in lay terms, is the amount of power an energy source has per unit volume. Crucially, power is a measurement of time rate of energy transfer. The higher the power density, the faster the rate of energy transfer (which results in a faster recharge time.)

Additionally, the SMC design has shown to have an energy density of 160 Watt-hour/kgcell, which is comparable to commercial Li-ion batteries and 30 times higher than that of conventional supercapacitors. The greater the energy density, the more energy the device can store for the same volume (resulting in a longer driving range for electric vehicles). Again, here the massive graphene structures of the prototype cells have not yet been optimized, so potential exists for even greater energy density in future iterations.


While most research into energy storage in either battery or supercapacitor technology has focused on either improving the power density of lithium-ion batteries or increasing the energy density of supercapacitors, both approaches have significant inherent challenges. By creating a fundamentally new paradigm in energy storage, SMCs could allow researchers to circumvent those issues.

The elegance of SMC design is its ability to bridge the gap between relatively long-range but slow charging Li-ion batteries and fast charging but distance-challenged supercapacitors. Researchers might finally have a method to create both high power and energy dense cells without sacrificing one for the other.

The critical difference between an SMC and a battery is that the ions in an SMC exchange rapidly between graphene surfaces, instead of moving laborously through the bulk of the electrode as in a typical lithium-ion battery. The time consuming process of intercalation – where the ions have to be inserted into the electrodes of a battery – is sidestepped with an SMC. The large surface area of the graphene cathode and the short distance the ions travel through the electrolyte permit the high observed energy and power densities. SMC cell lifetimes are still being explored, but so far observed cycling has shown no more than a 5% reduction of capacity.

While Angstrom Materials’ primary business is the sale of pricey graphene, it is engaged in massively scaling up graphene production to reduce the cost of the material dramatically over the next few years. As a result, the researchers on the project do not see any significant hurdles to overcome for commercialization to occur.

Unlike many other promised but unrealized breakthroughs in energy storage, the science and research behind SMCs is sound. With few major hurdles to overcome, the use of graphene cells could radically advance the promise of EVs in a short span of time. Assuming the technology reaches market, we could be looking back at charging times of the current crop of electrified vehicles as quaint within a decade. An electric car that charges back up in minutes? It could be the critical tipping point when EVs and plug-ins go from luxury to ubiquity.

Resources:

Bor Z. Jang, Chenguang Liu, David Neff, Zhenning Yu, Ming C. Wang, Wei Xiong, Aruna Zhamu (2011) Graphene Surface-Enabled Lithium Ion-Exchanging Cells: Next-Generation High-Power Energy Storage Devices. Nano Letters Article ASAP doi: 10.1021/nl201849

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